1. Field of the Invention
The present invention relates to a multi-layer ceramic lowpass filter particularly for use in a wireless communication terminal such as a portable phone or RF module.
2. Description of the Prior Art
The trends of wireless communication terminal are power saving and miniaturization. To correspond to those trends, a miniaturized lowpass filter with high performance is required.
FIG. 1 is a conventional lowpass filter 8, with its equivalent circuit shown in FIG. 2. The filter 8 comprises an inductor 4 and two capacitors 3, 5. The drawback of this filter 8 is that the capacitors 3, 5 in this filter 8 usually have a large value, especially for low frequency applications. As a result, it is impractical to implement a miniaturized lowpass filter by adopting this type of configuration.
FIG. 3 is another conventional lowpass filter 10, with its equivalent circuit shown in FIG. 4. The lowpass filter comprises inductors 13, 14, 15 and capacitors 16, 17. Branches of a serial inductor and capacitor contribute to an attenuation pole, which improves spurious response in higher frequency range. Due to the serial inductors 13, 15 the capacitors 16, 17 for this kind of filter 10 usually have much smaller value than those required in the filter 8 shown in FIG. 1. However, implementing the filter 10 in uniplanar form is still too large from the view of a mobile device.